In recent years, the spread of ADSL, FTTH, and other broadband networks are notable. Moreover, we can see a rapid spread in an IP telephone service for transmitting voices in a form of IP packets by utilizing a property of the broadband network, namely a high-speed transmission.
In the IP telephone service, speech communication voice data is sent or received between terminals having IP addresses on a TCP or UDP/IP layer in a Voice over IP (VoIP: for example, ITU-T Recommendation H.323, which is nonpatent literature 1 described below) protocol or the like. Therefore, it is necessary to convert a telephone number to an IP address. Nowadays, a session initiate protocol (SIP: RFC2543, which is nonpatent literature 2 described below) proxy server is generally used for the conversion from the telephone number to the IP address.
In the IP telephone communication using SIP, an input of a telephone number at a calling terminal causes sending of a session request message including a destination telephone number to the SIP proxy server (hereinafter, referred to as SIP proxy). Upon receiving the session request message, the SIP proxy acquires an IP address of a called terminal in the opponent party by performing necessary processing such as searching a domain name system (DNS: RDC1035) server. It then makes initial connection between the calling terminal and the called terminal as a proxy. The called terminal sends a response message in response to the session request message. Both of the messages are text streams represented by text (character codes).
The primary part of the SIP message is described in a format similar to a header description format of e-mail or the like such as “attribute: value”, and in order to identify mutual functions of the terminals, it is possible to describe a processing function (a communication function) about a media stream of a terminal of interest in a format conforming to a session description protocol (SDP: RFC 2327, which is nonpatent literature 3 described below). The following shows an example of a declaration (offer) of the calling terminal in SDP described in an appendix of RFC2543 titled “B.1 Configuring Media Streams.”
v=0
0=alice 2890844526 2890844526 IN IP4 host.anywhere.com
c=In IP4 host.anywhere.com
m=audio 49170 RTP/AVP 0
a=rtpmap:0 PCMU/8000
m=video 51372 RTP/AVP 31
a=rtpmap:31 H261/90000
m=video 53000 RTP/AVP 32
a=rtpmap:32 MPV/90000
As stated above, SDP is formed by arranging a single-character mnemonic (v, o, c, m or the like) followed by “=” and subsequently arranging text representation values delimited by a blank or a slash. Particularly, in the above, mnemonic “m” can be used to represent a type of a media stream that can be processed by the terminal such as audio or video (“v,” “o,” and “c” are for use in identifying a protocol version, identifying an initiator or an owner of a session (or message) at issue, and describing various connection information, respectively).
On the other hand, facsimile machines have been used as devices capable of sending or receiving image data easily before the spread of the IP network such as the Internet. A facsimile machine is capable of sending image data to a station in the opponent party very easily only by a specification of a telephone number. It is still widely used even at the present time when people can send images via e-mail from a PC, a mobile phone, or any other terminal.
In the future, an image communication apparatus such as a facsimile machine will need be capable of communication using various image communication systems as described later as well as communication via a public switched telephone network (PSTN: Non-IP network) independently of whether it is for use in home or office.
For example, at present, a so-called Internet facsimile protocol described in ITU-T Recommendation T.37 or T.38 is well known as a procedure for using the facsimile machine for communication on an IP network. In the Internet facsimile protocol described in these Recommendations, sending and receiving terminals are required to use the IP network directly or indirectly.
On the IP network, if there is no need to use a facsimile-related procedure, image data can be sent or received by using a faster system such as, SMTP, FTP, HTTP, RCP, IPPFAX or any other general data sending/receiving protocol on the IP network.
A facsimile signal in the conventional facsimile protocol is an analog speech signal. Therefore, it is also possible for both of a calling party and a called party to conduct image communication by sending or receiving facsimile data in an analog speech signal format on the IP network by using the above VoIP technology (so-called considered-speech Internet facsimile communication).
Naturally, if a station in the opponent party is a facsimile machine connected to a PSTN (non-IP network), it is necessary for a calling party to perform the facsimile communication in the conventional facsimile protocol (for example, T.30 protocol). In the image communication using the conventional facsimile protocol such as the T.30 protocol, there are two assumable cases: one is a case where both of the calling and called terminals conduct communication via the PSTN and the other is a case where the calling party accesses the IP network and sends a facsimile signal with considered speech by means of VoIP communication. In both cases, a reliable execution of image communication is required.
At the present stage, however, there are not a few image communication apparatuses having various and many image communication systems implemented as stated above: even if a plurality of image communication systems can be used in an apparatus, it requires a complicated operating procedure or setup in most cases. For example, there are complications at present such that at least it is necessary to specify which system should be used among the above image communication systems for each called party and that a user has to check communication systems that the called party can use, in advance.
In view of these problems, there may be an arrangement that the above SIP service is used at least regarding the communication via the IP network so that both terminals mutually identify applicable image communication systems (for example, T.37 facsimile communication, T.38 facsimile communication, SMTP, FTP, HTTP, RCP, IPPFAX or any other general-purpose IP protocol communication, considered-speech Internet facsimile communication) using an SDP media stream description in an SIP message.
It has, however, a problem that a media stream defined by the current RFC2327 is limited to a range of an image (particularly, an animation or motion picture stream for use in a video (or TV conference) and a speech stream and therefore it is insufficient to identify various image communication systems such as the T.37 facsimile communication, the T.38 facsimile communication, the SMTP, FTP, HTTP, RCP, IPPFAX or any other general-purpose IP protocol communication, the considered-speech Internet facsimile communication.
In addition, if image communication is conducted by using the above SMTP, FTP, HTTP, RCP, IPPFAX or any other IP service, instead of the facsimile protocol, generally a format of a transferred data file is not assured in these protocols. Therefore, there has been a problem such that, for example, it is impossible to exchange information about a paper size available for print processing at the receiving terminal and an applicable image compression technology or other capabilities of the terminal. Therefore, even if the receiving terminal receives image data, it cannot decode the image data or cannot perform optimum output processing (printing or the like) for the image.